M3: live ingestion (MQTT/Tasmota + Home Assistant)

- PayloadExtractor: dot-path value/time extraction (Tasmota ENERGY.Total, bare scalars).
- MqttTopicMatcher: standard +/# wildcard matching.
- IngestionService: scale/offset, idempotent upsert on (meter_id, time), and a spurious-
  decrease guard for monotonic registers (allowed only with a reset/swap event) + source
  last-seen status.
- MqttMessageRouter + MqttIngestionWorker (MQTTnet 5): per-endpoint persistent connections,
  topic subscription, graceful degradation; secrets resolved by env-var reference.
- Home Assistant: HaStateClient (REST /api/states parse) + HomeAssistantWorker polling on
  each source's interval. HA-via-MQTT also works through the MQTT path.
- Ingestion workers gated by MeterVault:EnableLiveIngestion (off in tests).

85 tests green (53 Core + 32 integration): Tasmota payload → reading verified end to end.

Follow-up (polish): HA WebSocket push (state_changed) as an alternative to REST poll;
source-topic index caching in the router.

Claude-Session: https://claude.ai/code/session_01WujdMtMJPbxDpDnMeK22rr

tests/Integration.Tests/MeterVaultAppFactory.cs

@@ -14,5 +14,6 @@ public sealed class MeterVaultAppFactory(string connectionString) : WebApplicati
         builder.UseEnvironment("Testing");
         builder.UseSetting("ConnectionStrings:Default", connectionString);
         builder.UseSetting("MeterVault:RunMigrationsAtStartup", "false");
+        builder.UseSetting("MeterVault:EnableLiveIngestion", "false");
     }
 }